(a) Field of the Invention
The present invention relates to a liquid droplet spraying apparatus and method, and more particularly to a liquid droplet spraying apparatus and method which can minutely and efficiently spray fluid in the form of a liquid droplet by applying an electrostatic field to a surface of the fluid sprayed through a nozzle and accessorily applying a physical spraying force.
(b) Description of the Related Art
Generally, a liquid droplet spraying apparatus for spraying fluid in the form of the liquid droplet has been variously applied to an inkjet printer, and has recently been applied and developed to be used in a state-of-the art high value-added field such as a display process apparatus, a printed-circuit-board process apparatus, and a deoxyribonucleic acid (DNA) chip manufacturing process.
In the inkjet printer, an ink spraying apparatus for spraying ink in the form of a liquid droplet is divided into a thermal driving type and an electrostatic type.
First, as shown in FIGS. 1 and 2, the thermal driving type ink spraying apparatus includes a manifold 22 provided in a substrate 10, an ink channel 24 and an ink chamber 26 defined and constrained by a partition wall 14 formed on the substrate 10, a heater 12 provided in the ink chamber 26, and a nozzle 16 provided in a nozzle plate 18 and spraying an ink droplet 29′. Such a thermal driving type ink spraying apparatus sprays the ink droplet 29′ through the following operations.
The heater 12 generates heat when receiving voltage, and thus ink 29 contained in the ink chamber 26 is heated while generating bubbles 28.
Then, the generated bubbles 28 are continuously expanded, and pressure is applied to the ink 29 contained in the ink chamber 26, so that the ink droplet 29′ can be sprayed by the nozzle 16 to the outside of the nozzle 16.
Then, the ink 29 is absorbed from the manifold 22 to the ink chamber 26 via the ink channel 24, so that the ink chamber 26 can be recontaining the ink 29.
However, as described above, a conventional thermal driving type ink spraying apparatus may cause the ink 29 to be chemically changed by the heat of the heater for forming the bubbles, and therefore have shortcomings that a problem such as deterioration in quality of the ink 29 may arise.
Also, the droplet 29′ of the ink sprayed through the nozzle 16 may be is rapidly changed in volume due to heat of the heater 12 while moving toward an object such as paper, and also have a problem of deterioration in print quality such as resolution.
Further, the thermal driving type ink spraying apparatus has a problem that there is a limit to minute control for the ink droplet 29′ sprayed through the nozzle 16, e.g., control for the size and shape of ink droplet.
The above problems bring another problem of difficulty in embodying a high-integration liquid droplet spraying apparatus.
Meanwhile, FIGS. 3 and 4 illustrate another type of a liquid droplet spraying apparatus, i.e., an electrostatic type liquid droplet spraying apparatus using an electric field.
More specifically, as shown in FIGS. 3 and 4, the electrostatic type liquid droplet spraying apparatus includes a base electrode 32 and an opposite electrode 33 placed opposite the base electrode 32. Ink 31 is contained between the two electrodes 32 and 33, and a direct current (DC) power source 34 is connected to the two electrodes 32 and 33.
When voltage is applied from the DC power source 34 to the electrodes 32 and 33, an electrostatic field is formed between the two electrodes 32 and 33.
Thus, Coulomb's force is applied to the ink 31 in a direction toward the opposite electrode 33.
On the other hand, the ink 31 has a repulsive force to the Coulomb's force the ink 31 because of its own surface tension, viscosity, etc., and is thus not easy to be sprayed in the direction toward the opposite electrode 33.
Accordingly, in order to separate a liquid droplet from the surface of the ink 31 and spray it, a very high voltage of 1 kV or higher has to be applied between the electrodes 32 and 33.
However, if high voltage is applied between the electrodes 32 and 33, the liquid droplet is very irregularly sprayed and therefore a predetermined portion of the ink 31 is locally heated.
That is, temperature T1 of ink 31′ located in a region S1 increases higher than temperature T0 of ink 31 located in other regions. Therefore, the ink 31′ of the region S1 is expanded, and the electrostatic field is concentrated on this region so that a lot of electrons can be collected in this region.
Since the repulsive force between the electrons and the Coulomb's force based on the electrostatic field are exerted upon the ink 31′ of the region S1, a liquid droplet is separated from the ink 31′ of the region S1 and moves toward the opposite electrode 33 as shown in FIG. 4.
FIG. 5 shows an electrostatic type ink spraying method. There is a nozzle 4 provided with an electrode 6, and an opposite electrode 7 is placed under a substrate 8, so that a liquid droplet can be discharged and sprayed to a substrate 8 on the foregoing principle. Voltage is applied by supplying DC power in the form of pulse between the electrode 6 of the nozzle 4 and the opposite electrode 7.
In such a manner, there have been continuously reported research results and relevant antecedent patents that show successful jetting and patterning.
However, the above electrostatic type liquid droplet spraying apparatus has the following problems or shortcomings to be overcome. There are problem that the very high voltage of 1 kV or higher has to be applied to the electrode 6, the nozzle 4 has to be internally provided with the electrode, and the opposite electrode 7 has to be externally provided in a nozzle direction or under the substrate 8. To place the electrode 6 inside the nozzle 4, a very complicated process is needed. Also, while discharging the liquid droplet in a direction toward the opposite electrode 7, there may be instability that a single liquid droplet may be shredded and sprayed. In the case that the nozzle 4 approaches the substrate 8 in order to improve directionality of a liquid droplet, there is a limit to an approaching distance because of an electrical breakdown. Since the discharged liquid droplet basically possesses an electrical charge, there is force acting between a liquid surface existing on the nozzle 4 and the substrate 8, and thus a moving direction of the liquid droplet is distorted in the vicinity of the substrate. Last, an electric current flowing in the ink may cause an electro-chemical reaction.